The air pointers may have diverse functions, notably: remote control of an audiovisual apparatus (television, reader/recorder of disks, hi-fi system), where the point is a program or a function to be chosen from a menu; remote control of a household apparatus where the pointer designates the apparatus and has it execute a function; computer remote control where the pointer is programmed as a function of the applications executed by the computer; electronic games interface where, depending on the game, the pointer may be an object manipulated by the user (golf club, tennis racket, bowling ball, handgun, hip gun or rifle, etc.); assistance for the man-machine interface or remote control intended for persons with reduced mobility (for example, fixing of a pointer to the head, the spectacles, an earpiece, or any other part tied to the movements of the head, so as to aid persons with motion deficiency or who are unable to use a conventional hand-held mouse to direct a pointer at the screen). In general, the pointer is equipped with buttons which allow selection of a command, which can be programmed to execute a function (or a service) or to associate a different pointer state during the pointing gesture (trajectory with button pressed vs trajectory with button released, thereby making it possible for example to take as information not the situation of a point on the screen but a cursor trajectory that may itself be associated with an action, etc.).
The movements of the pointer in space comprise rotations and translations. They can be measured by sensors of various types: image sensors can measure rotations and translations at one and the same time by comparison of successive images and geometric transformations; a magnetometer, an accelerometer or a single-axis gyrometer can measure a rotation about said axis; a combination of magnetometers, accelerometers and/or of gyrometers can measure the translations and rotations about several axes; a combination of sensors of the previous types improve measurement accuracy, redundancy allowing determination of confidence intervals; the combination can comprise one or more cameras and several magnetometric, accelerometric and/or gyrometric sensors.
Another rotation sensor, insensitive to accelerations, may be a brightness sensor. If it is a photoelectric cell, it is known that the amount of light received by said cell is proportional to its light receiving area and to the cosine of the angle of inclination of the rays with its normal. The light source may be the sun, or some other quasi-pointlike source, bulb type, situated far enough away for its emission rays to be considered parallel to one another over the whole of the volume of the gestural experience. To avoid problems of changeable ambient brightness, it is advantageously possible to use a “fly's eye” multi-facet type sensor, the angular direction of reception being the facet which measures the highest luminous flux.
The general problem that these applications of motion sensing pointers must solve is to take account of the manner in which the user holds the pointer, in particular of the orientation thereof in space. Indeed, if the pointer is held for example at 45° instead of being held horizontally, a horizontal or vertical motion of the pointer will be conveyed on the screen at which it points by a diagonal motion. This phenomenon is known by the name “tilt” or torsion. It should therefore be corrected in order for the pointer to be usable.
A first procedure for solving this problem is to provide mechanical means so that the sensors remain in a substantially fixed position in the frame of reference of the screen when the user imparts a torsion motion to the pointer. It is thus possible to provide for the sensor or sensors to be mobile within the pointer in the manner of a pendulum whose base has sufficient inertia to remain substantially fixed in spite of the torsion movements imparted to the pointer. Such a device is disclosed by U.S. Pat. No. 5,453,758, which is incorporated by reference herein. It is also possible to encapsulate said sensors in a stabilization device consisting of a pair of spheres tied to the pointer by rotation axles, as is the case in a compass aboard a boat or an aircraft. Such a device is disclosed by U.S. Pat. No. 5,440,326, which is incorporated by reference herein. A first drawback of these mechanical devices for compensating for the torsion of the pointer is that they are limited to restricted spans of angles of torsion and of rate of displacement. A second drawback is that these devices are bulky. A third drawback resides in the mechanical inertia of these devices and the delay in the horizontal alignment induced, thus barring them from real-time pointing applications.
A second procedure for compensating for this torsion of the pointer consists in computing the angles of torsion by using the measurements of some of the sensors embedded aboard the pointer, notably accelerometers, and to thereafter perform a transformation of the measurements of the other sensors from the frame of reference of the pointer into that of the screen by applying to said measurements one or more rotation matrices whose coefficients are dependent on the torsion angle or angles. Such procedures are disclosed notably by patent U.S. Pat. No. 5,902,968, which is incorporated by reference herein where the main sensor is a gyrometer and the sensor for computing the angles of torsion is an accelerometer, patent application US 2004/0075650, which is incorporated by reference herein where the main sensor is a camera coupled to accelerometers, the combination allowing tilt correction, patent application US 2002/0140745, which is incorporated by reference herein where the main sensor is a GPS receiver and the tilt correction sensor a set of accelerometers and patent U.S. Pat. No. 7,158,118, which is incorporated by reference herein where the main sensor consists of one or more gyro meters and the tilt correction sensor consists of one or more accelerometers. This procedure has the drawback of providing noisy results insofar as the torsion angles are computed by using trigonometric calculations which are not adapted to fixed point/small memory processors which are preferably used in low cost air pointing devices.
A new way of correcting the tilt has been disclosed by US patent application published as US2009/0326857 to the assignee of the present application, which is incorporated by reference herein. According to this invention, instead of computing the tilt angle with the canonic trigonometric formulas, the measurements of the accelerometers are directly used to correct the measurements of the gyro sensors.
It has been found, though, that it may be advantageous to use only one accelerometer measurement at a moment in time to accomplish the tilt correction, so as to simplify the calculation of the correction and use less computing power, which is then freed for other tasks. Also, when an accelerometer axis is close to the vertical, its measurements are noisy, the values close to 1 lack precision and the roll correction along this axis is not accurate for angles higher than around 70°, leading to an overall bias affecting the cursor movements on the display.